1. Field of the Invention
The present invention relates to a transition metal compound, a polymerization catalyst using the same and a process for producing a styrenic polymer using said catalyst. More particularly, it pertains to a transition metal compound which is useful as a component of a polymerization catalyst for a compound containing an ethylenically unsaturated double bond or acetylene series, especially of a polymerization catalyst for styrene series; a highly active polymerization catalyst which contains the above-mentioned transition metal compound and serves for a compound containing an ethylenically unsaturated double bond or acetylene series; and a process for efficiently producing at a low cost, a styrenic polymer which has a high degree of syndiotactic configuration and is minimized in the amounts of residual metals by the use of the aforesaid polymerization catalyst.
2. Description of Related Arts
Olefinic polymers such as polyethylene and polypropylene find their great use as a general-purpose resin in a variety of fields. It is known that the aforesaid olefinic polymers are produced in the presence of a catalytic system containing Ziegler-Natta catalyst as a principal catalytic component. Recently an attempt is made to produce an olefinic polymer by the use of a polymerization catalyst comprising as a catalytic component, a transition metal compound having a .pi. ligand in which said .pi. ligand is bonded to a central metallic element through an arbitrary group.
For example, there are disclosed catalysts for olefins polymerization comprising as a catalytic component, a transition metal compound having a .pi. ligand in which said .pi. ligand is bonded to a central metallic element through an arbitrary group as well as processes for producing olefinic polymers by the use of the catalysts in European Patent Application Laid-Open Nos. 420436, 418044, 416815, 468651, 495375, 514828 and 520732, International Publication No. 00333/1992, etc.
However, sufficiently satisfactory catalytic-activity has not been obtained from a catalyst among them comprising a transition metal compound in which the .pi. ligand is a fused polycyclic cyclopentadienyl group containing an aromatic ring such as indenyl group or fluorenyl group.
Heretofore, styrenic polymers produced by the radical polymerization method or the like have an atactic configuration in stereostructure and are molded to various shapes by various molding methods such as injection molding, extrusion molding, blow molding, vacuum molding and cast molding, and they have been widely used as domestic electrical appliances, office machines, household goods, packaging containers, toys, furnitures, synthetic papers, sheets, films and other industrial materials.
However, such styrenic polymers having atactic configuration have disadvantage that it is inferior in heat resistance and chemical resistance. On the other hand, since the styrene polymers having a syndiotactic configuration have melting points which are different from those of the conventional atactic polystyrenes, and are higher than those of the isotactic polystyrenes known so far, they are expected to be used as heat-resistant resins in various fields.
The group to which the present inventors belong has previously found that the use of a combined catalyst of an aluminoxane with a transition metal compound having an indenyl group as a .pi. ligand can produce a styrenic polymer having a syndiotactic configuration (refer to Japanese Patent Application Laid-Open No. 294705/1989). However, the catalyst comprising the transition metal compound containing, as a .pi. ligand, a fused polycyclic cyclopentadienyl group having an aromatic ring such as an indenyl group suffers a disadvantage that the catalyst fails to attain a sufficient catalytic activity.